The invention relates to a hingeless rotor for helicopters wherein the lift producing sections of the rotor blades are connected at their inner ends to a respective intermediate member. The intermediate members are flexible to torsional and bending loads and tension resistant, whereby the intermediate members allow blade angle movements as well as flapping and lead-lag movements. Each intermediate member is secured to the rotor mast or drive shaft connector by a substantially rigid connecting element. Each blade section has a support or carrier bar or spar in common with the respective intermediate member and connecting element. The carrier spar is made of fiber compound material and extends as an integral element from the respective blade section to the rotor mast. The fibers of the carrier spar extend substantially unidirectionally relative to the longitudinal axis of the carrier spar.
Known types of rotor systems having a hingeless flapping and lead-lag blade connection require a special, rigidly constructed rotor head which is attached to the central rotor mast. An example of such a system is disclosed in the German Patent Publication No. 1,531,375. The rotor head of such rotor systems supports each of the rotor blades by means of blade angle bearings so that the rotor blades are rotationally movable. The rotor blades of such systems comprise a lift producing blade portion and a neck portion which is flexible to bending but torsionally resistant. Generally, such rotor systems also comprise additional tensionally resistant laminae connecting the rotor blades at the blade roots to each other in order to compensate for centrifugal force loads, and detachable, pivotally acting fittings arranged between the blade angle bearings and the bending and flexible blade neck portions for folding the rotor blades. Such rotor systems do achieve an exact steering function and a favorable positioning of the so-called fictive flapping hinges in the area of the bending-elastic neck portions and with a comparitively large spacing from the axis of rotation of the rotor. However, such rotor systems have a relatively complicated structure, are produced by a rather complicated method of construction and have a correspondingly large structural weight because of the need for a specially constructed rotor head arrangement with blade angle bearings and possibly with tension members.
In contrast, rotor systems of the type mentioned above at the beginning, an example of which is described in U.S. Pat. No. 3,669,566 do not require a special rotor head nor do they require any blade angle bearings other than the flapping and lead-lag hinges. Each of the lift producing sections of the rotor blades of such rotor systems are connected directly to the rotor mast by means of a support spar which is connected at one end to the rotor mast and the other end of which extends into the lift producing portion of the rotor blade. The support spar comprises a plurality of individual fibers made of fiber compound material. The individual fibers are combined to form an integral structural member connected on one end to the rotor mast and on the other end to the lift producing portion of the rotor blade. The fibers of the support spar in the bending and torsionally elastic region between the rotor mast and the blade section, are spaced from one another and uniformly distributed over the entire cross section of the support spar. In this region the fibers are embedded in an elastomeric material. A folding of the rotor blades of such a rotor system is not possible, however, because of the single piece of integral construction of the support spar extending from the rotor mast into the lift producing portion of the rotor blade. Non-folding rotor blades are disadvantageous, particularly when the rotor blade diameter is large. Besides, the fictive flapping and lead-lag hinges are located unfavorably close to the rotor center because of the small radial spacing of the bending-elastic intermediate region from the axis of rotation of the rotor. Primarily, however, the intermediate region of the support spar is not only elastic to bending and to torsional loads, it is also unstable against shearing loads to a high degree. Consequently, the intermediate blade region of such a rotor system is subject to uncontrollable deformations and transverse displacement of the blade axis due to the effect of transverse forces on the rotor blade, primarily the forces due to lift and air resistance. Such deformations and transverse displacements have a highly disadvantageous effect on the steering or control behavior of the rotor system.